The invention is based on a device for measuring the mass of a flowing medium as defined hereinafter. European patent 0 087 621 discloses a device in which to measure the mass of a flowing medium, particularly the intake air mass of an internal combustion engine, a measuring element, for example in the form of a hot wire, is disposed in a bypass conduit that is offset from a main intake conduit. Considerable fluctuations or pulsations of the flow velocity arise in the bypass conduit from the opening and closing of the injection valves of the individual cylinders of the engine, the intensities of which depend upon the intake frequency of the individual pistons or the engine speed. These flow fluctuations, namely the flow velocity prevailing on average in the bypass conduit and the intake air mass of the engine that can be calculated from it, distort the measuring result considerably, and in fact in such a way that depending on the intensities of the pulsations of the flow velocity, for example in the partial load range of the engine, the result may be an overly low reading for the mean flow velocity, and a overly high reading when the throttle valve is completely open. In the device mentioned at the beginning, longitudinal and cross sectional proportions of the main intake conduit and bypass conduit are chosen in order to reduce these measurement errors, which arise only during pulsating flow, these proportions being arrived at by means of calculations and numerous measurements; the position of the measuring element in the bypass conduit is specified. On the one hand, this considerably reduces the structural design and installation options for the device, and on the other hand, the embodiment of the device with a bypass conduit requires a large space, so that when the available installation space is tight, particularly in the intake region of the engine, it is only limitedly possible to install the device.
German patent document 28 45 661 discloses a device in which a hot wire is provided as a temperature-dependent measuring element; it is disposed in a measuring conduit, in a medium to be measured, by means of an securing sleeve. The securing sleeve is necessary in order to tender the hot wire by means of support hooks on the inside wall of the securing sleeve. The securing sleeve has a relatively small inside diameter so that on the one hand the flow past it is nearly unchecked between an outer face of the securing sleeve and an inner wall of the measuring conduit without being influenced by the securing sleeve, and on the other hand, a flow aligned as parallel as possible on the inside of the securing sleeve bathes the hot wire; the variance of the measurement value described at the beginning sets in when the flow pulsates.